The mechanical and volumetric behaviour of sisal fibre reinforced concrete blocks

[摘要] ENGLISH ABSTRACT: Natural fibre reinforced concrete (NFRC) is a type of concrete that has become of particular interestin recent years, due to its potential for being used as a sustainable and economically viable buildingmaterial. Natural fibres are often cheap and widely available in developing nations. Sisal is one suchfibre predominantly grown in Brazil and has been identified as having the potential to becommercially cultivated in Southern Africa.The durability of sisal fibres in a cementitious environment tends to be adversely affected due to thehigh alkalinity of pore water and the presence of calcium hydroxide.This research dealt with the use of sisal fibre reinforced concrete (SFRC) blocks. It focused on themechanical and volumetric properties of blocks with varying fibre and condensed silica fume content(CSF).Two different SFRC blocks were produced (solid and hollow) using an average fibre length of 10 mm.Two matrix types were used: one using a 70:30 cement:fly-ash ratio and another using a 60:30:10cement:fly-ash:CSF ratio by weight. Samples of each matrix type were prepared with 0, 0.5 and 1%fibre content by volume.Hollow blocks were tested for compressive strength and capillary water absorption, while solidblocks were tested for compressive strength, flexural strength, capillary water absorption,dimensional stability, drying shrinkage, density, total water absorption and void content. All testswere performed on samples with an age of 28 days. Solid block compressive tests were alsoperformed on samples with an age of 7 days.The hollow blocks had significantly lower average compression strength than the solids, but anincrease in fibre content caused a slight increase in strength.For solid blocks, it was found that the addition of natural fibres decreases the strength, although apartial substitution of cement with CSF, in conjunction with fibres, did increase the strength relativeto blocks without CSF. The flexure strength was also lowered somewhat by the addition of fibres, butan increase in ductility was noted, although not quantified.The addition of CSF to fibre-containing blocks led to an increase in capillary water absorption, but adecrease in absorption through immersion. This shows that the addition of CSF does significantlyalter the pore system of a cementitious matrix reinforced with natural fibres.Also, the dimensional stability increased with the addition of CSF and fibres. The same can be said fordrying shrinkage. Even though an increase in fibre and CSF caused samples to shrink more underdrying, they were more stable under cycles of wetting and drying.It was concluded that the addition of fibres to a matrix had a detrimental effect on strength,although ductility did increase. The volumetric properties of concrete were also adversely affected bythe addition of fibres, although dimensional stability was improved. The partial substitution ofcement with CSF did improve many of the mechanical and volumetric properties of samplescontaining sisal fibre.

[发布机构] Stellenbosch University